Examine source code of Highlight 7

{
  "manifest_version": 2,
  "name": "Highlight 7",
  "author": "xenkuo@gmail.com",
  "description": "A simple and graceful tool that highlights max 7 words.",
  "version": "1.1.4",
  "default_locale": "en",
  "applications": {
    "gecko": {
      "id": "highlight-7@xenkuo.com",
      "strict_min_version": "57.0a1"
    }
  },
  "permissions": [
    "<all_urls>",
    "activeTab",
    "storage",
    "menus"
  ],
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_icon": {
      "16": "icons/hl-7.png",
      "32": "icons/hl-7@2x.png",
      "48": "icons/hl-7@3x.png",
      "96": "icons/hl-7@6x.png"
    }
  },
  "commands": {
    "auto": {
      "suggested_key": {
        "default": "Alt+Shift+2",
        "mac": "Command+Shift+2"
      },
      "description": "Highlight word with auto color"
    },
    "clear": {
      "suggested_key": {
        "default": "Alt+Shift+X",
        "mac": "Command+Shift+X"
      },
      "description": "Clear all highlight words"
    },
    "switch": {
      "suggested_key": {
        "default": "Alt+Shift+E",
        "mac": "Command+Shift+E"
      },
      "description": "Switch highlight 7 on/off"
    }
  },
  "icons": {
    "16": "icons/hl-7.png",
    "32": "icons/hl-7@2x.png",
    "48": "icons/hl-7@3x.png",
    "96": "icons/hl-7@6x.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}